The subject matter disclosed herein relates to non-invasive imaging and, in particular, to spectral calibration of a radiographic imaging system.
In the fields of medical imaging and security screening, non-invasive imaging techniques have gained importance due to benefits that include unobtrusiveness, convenience, and speed. In medical and research contexts, non-invasive imaging techniques are used to image organs or tissues beneath the surface of the skin. Similarly, in industrial or quality control (QC) contexts, non-invasive imaging techniques are used to examine parts or items for hidden defects that may not be evident from an external examination. In security screening, non-invasive imaging techniques are typically used to examine the contents of containers (e.g., packages, bags, or luggage) without opening the containers and/or to screen individuals entering or leaving a secure location.
One example of a non-invasive imaging system is a computed tomography (CT) imaging system in which an X-ray source emits radiation (e.g., X-rays) towards an object or subject (e.g., a patient, a manufactured part, a package, or a piece of baggage) from a variety of different angular positions. The emitted X-rays, after being attenuated by the subject or object, typically impinge upon an array of radiation detector elements of an electronic detector, which generates signals indicate of the incident radiation at different locations on the detector. The intensity of radiation reaching the detector is typically dependent on the attenuation and absorption of X-rays through the scanned subject or object. The signals generated at the detector are processed to generate images and/or volumetric representations of the internal structures of the subject or object.
Such a CT system may be subject to various artifacts, such as beam hardening artifacts, ring/band artifacts, and/or scatter-induced artifacts. To mitigate such artifacts, a spectral calibration process may be performed using a variety of calibration phantoms. However, as the scan coverage of such CT systems has increased (particularly in the dimension extending through the imaging bore, i.e., the Z-direction), the phantoms have grown correspondingly larger to accommodate the increased scan coverage. The increased size of such calibration phantoms can make performing spectral calibrations by attaching the phantom at the edge of the patient table increasingly difficult.